Max Greyserman eagled the par-5 15th hole to seize a two-stroke lead after Sunday's third round of the rain-hit PGA Wyndham Championship.
World number 76 Greyserman, a PGA Tour rookie, fired a four-under par 66 to leave the 29-year-old American on 15-under 195 for 54 holes, with US amateur Luke Clanton second on 197 after firing a 62.
Threesomes remained in their pairings in a bid to complete the final round before darkness fell at Sedgefield Country Club in Greensboro, North Carolina.
A tropical storm that dumped more than 15 centimetres of rain on the course wiped out play on Thursday and set the stage for finishing the second round on Sunday and trying to then complete 36 holes before sunset.
In the final regular-season event before next week's start of the PGA playoffs, 36-hole leader Matt Kuchar – the only player to compete in every playoff since the system began in 2007 – needed a win to continue the run.
Only the top 70 in season points after the final round will qualify for the playoffs.
Kuchar was in a third-place pack on 198 that also included Americans Ben Griffin, Davis Thompson and Cameron Young, Japan's Ryo Hisatsune and England's Aaron Rai.
Kuchar made a 12-foot birdie putt at the first hole, sank a 27-footer to birdie the sixth and made a 10-footer for birdie at the eighth but missed the green on the par-3 12th and made bogey, leaving him on 14-under and ahead by only one shot.
When Kuchar took a bogey at 14 after finding the right rough off the tee, he fell into a share of the lead with Greyserman on 13-under.
Greyserman, who birdied the par-5 fifth and par-4 10th from about 2.4 metres to stay with Kuchar, seized the lead when he eagled the par-5 15th from just inside seven feet to reach 15-under.
Greyserman curled in a 19-foot par putt at the 18th to keep his margin entering the final round.
Clanton's 62 was his PGA-best third round of 63 or under since June, when he made his PGA debut at the US Open.
Clanton made two eagles on his opening nine, becoming the first amateur to eagle par-4 and par-5 holes in the same round since Doug Ghim at the 2018 Masters.
Clanton, runner-up in last month's PGA John Deere Classic in Silvis, Illinois, holed out from the fairway from 129 yards for eagle at the par-4 13th then answered a bogey at 14 with a six-foot eagle putt at the par-5 15th.